linux-kernel - Re: [PATCH] m68k: atari: Make Atari ROM port I/O write macros return void

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Message-ID: <286a1eef-e857-a31f-839b-00a4c835dfa9@roeck-us.net>
Date:   Fri, 20 May 2022 07:52:36 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org
Cc:     linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] m68k: atari: Make Atari ROM port I/O write macros return
 void

On 5/20/22 07:32, Geert Uytterhoeven wrote:
> The macros implementing Atari ROM port I/O writes do not cast away their
> output, unlike similar implementations for other I/O buses.
> When they are combined using conditional expressions in the definitions of
> outb() and friends, this triggers sparse warnings like:
> 
>      drivers/net/appletalk/cops.c:382:17: error: incompatible types in conditional expression (different base types):
>      drivers/net/appletalk/cops.c:382:17:    unsigned char
>      drivers/net/appletalk/cops.c:382:17:    void
> 
> Fix this by adding casts to "void".
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
> Survived m68k/allmodconfig.
> To be queued in the m68k tree for v5.19.
> 
> Removing the casts instead causes issues with functions propagating void
> return values (return expression in void function), which BTW sparse
> complains about, too.

We live and learn. I didn't even know that this was valid syntax.
I thought it might be easier to just fix that code, but coccinelle
reports that there are hundreds of places in the kernel where this
is done. Outch.

Guenter